terminology: call them null-terminated strings

Updated terminology in docs, comments and phrases to refer to C strings
as "null-terminated". Done to unify with how most other C oriented docs
refer of them and what users in general seem to prefer (based on a
single highly unscientific poll on twitter).

Reported-by: coinhubs on github
Fixes #5598
Closes #5608

src/tool_getparam.c

@@ -966,7 +966,7 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
         if(*p) {
           /* if there's anything more than a plain decimal number */
           rc = sscanf(p, " - %6s", lrange);
-          *p = 0; /* zero terminate to make str2unum() work below */
+          *p = 0; /* null-terminate to make str2unum() work below */
         }
         else
           rc = 0;
@@ -1517,7 +1517,7 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
         /* Automatic referer requested, this may be combined with a
            set initial one */
         config->autoreferer = TRUE;
-        *ptr = 0; /* zero terminate here */
+        *ptr = 0; /* null-terminate here */
       }
       else
         config->autoreferer = FALSE;

src/tool_getpass.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -238,7 +238,7 @@ char *getpass_r(const char *prompt, /* prompt to display */
   fputs(prompt, stderr);
   nread = read(fd, password, buflen);
   if(nread > 0)
-    password[--nread] = '\0'; /* zero terminate where enter is stored */
+    password[--nread] = '\0'; /* null-terminate where enter is stored */
   else
     password[0] = '\0'; /* got nothing */
 

src/tool_parsecfg.c

@@ -173,7 +173,7 @@ int parseconfig(const char *filename, struct GlobalConfig *global)
       /* ... and has ended here */
 
       if(*line)
-        *line++ = '\0'; /* zero terminate, we have a local copy of the data */
+        *line++ = '\0'; /* null-terminate, we have a local copy of the data */
 
 #ifdef DEBUG_CONFIG
       fprintf(stderr, "GOT: %s\n", option);
@@ -203,7 +203,7 @@ int parseconfig(const char *filename, struct GlobalConfig *global)
           line++;
 
         if(*line) {
-          *line = '\0'; /* zero terminate */
+          *line = '\0'; /* null-terminate */
 
           /* to detect mistakes better, see if there's data following */
           line++;
@@ -329,7 +329,7 @@ static const char *unslashquote(const char *line, char *param)
     else
       *param++ = *line++;
   }
-  *param = '\0'; /* always zero terminate */
+  *param = '\0'; /* always null-terminate */
   return line;
 }
 

src/tool_writeout.c

@@ -131,7 +131,7 @@ void ourWriteOut(CURL *curl, struct OutStruct *outs, const char *writeinfo)
             continue;
           }
           keepit = *end;
-          *end = 0; /* zero terminate */
+          *end = 0; /* null-terminate */
           for(i = 0; variables[i].name; i++) {
             if(curl_strequal(ptr, variables[i].name)) {
               match = TRUE;